How would you calculate the change in entropy when the pressure of a perfect gas is changed isothermally from P_i to P_f
Answer:
ΔS = nRIn(P_i/P_f)
Explanation:
Formula for entropy change is;
ΔS = nC_p•In(T_f/T_i) + nRIn(P_i/P_f)
Since the pressure of the perfect gas is changed isothermally, it means that temperature remains the same and as such T_f = T_i
Thus, we now have;
ΔS = nC_p•In(1) + nRIn(P_i/P_f)
In(1) = 0
Thus;
ΔS = nRIn(P_i/P_f)
